The invention relates to devices that use sonar to automatically control the delivery of electromagnetic radiation, including heat and light, to a target. In a preferred embodiment, the invention relates to sonar control of the delivery of radiant heat to the skin for the measurement of pain tolerance limits.
In applications where electromagnetic radiation (EMR) projected from an emitter is directed at a target, under conditions where distance may undesirably change between emitter and target, there is a need for automatic control processes that regulate the delivery rate of the EMR received at the target by adjusting the output of the emitter mechanism, the projector of heat or light or other EMR.
A true feedback mechanism would use a sensor, positioned at or within the target, to feedback-control either the power output or positionxe2x80x94the emitter-target distancexe2x80x94of the emitter, thus ensuring that these characteristics of the emitter are rapidly and automatically adjusted to maintain target (and sensor) irradiation within set limits.
Unfortunately, available sensor response characteristics are largely inadequate to this task. Thus, should a temperature sensor within the target be used to feedback control a motor-drive positioning mechanism (for instance) on which a radiant heat projector (emitter) is mounted, and the feedback from the sensor be used to control projector position, either toward or away from the target, it is found that accurate, rapid and responsive positioning of the emitter by the motor drive cannot be achieved because the sensor response time is invariably too slow, having too much inertia or resistance to change. The same is true of light and other forms of EMR.
When the emitter is employed as a sensory stimulator for testing human cutaneous sensibility, it is essential that the energy delivered to the skin be precisely controlled. Since delivered energy is a proportional function of the power of the emitter and the distance of the emitter to the skin target, both must be held constant to achieve adequate stimulus control. An earlier form of the computerized Heatbeam Dolorimeter (HBD) achieved this control by means of a precisely regulated power supply to the emitter, an infra-red (or heat or light) emitter, coupled with an articulated arm which allowed accurate positioning and an arrangement of intersecting visible lasers for guiding the precise positioning of the device at the correct emitter-target distance (Lipman J., U.S. Pat. No. 5,941,833).
Cutaneous sensory testing devices are employed in evaluating the state and the health of both the peripheral nervous system and the central nervous system and the central pain perceptual processes of the brain. Such testing devices employ some type of stimulus, either mechanical (tactile, pressure, vibration) thermal, electrical or of other modality, and assess the subject""s ability to detect and respond to the stimulus. Of particular relevance to the present invention is the sensory examination of the human pain continuum by means of sensory testing devices. The cutaneous range of pain sensation of the skin, called the xe2x80x98pain sensibility rangexe2x80x99 which is modality-specific, is bounded at the lower end of the stimulus intensity spectrum by the pain threshold, defined in terms of the stimulus intensity that is perceived as just noticeably painful by the subject. At the upper end of the pain sensibility range lies the pain tolerance limit, defined as the maximum possible pain stimulus intensity that the subject can tolerate. The pain tolerance limit has also been called the xe2x80x98reaction limitxe2x80x99 or xe2x80x98reaction thresholdxe2x80x99 by some authors (Hardy J D, Wolff H G, Goodell H (1952). Pain Sensations and Reactions, Williams and Wilkins Co, Baltimore, 1952), because it is accompanied by reflexive aversive withdrawal of the subject from the stimulus.
Tactile methods, such as that described in Horch et al. (U.S. Pat. No. 5,022,407 Apparatus for Automated Tactile Testing), apply stimulator elements or electrodes held in close physical contact with the skin, which transmit vibration or pressure or pin prick stimuli. Thermal methods, of which a preferred embodiment of the present invention is a particular variation, transmit heat to the skin either through a peltier-type heating electrode in contact with the skin (see: Lautenbacher S and Rollman G B (1991) Sex differences in responsiveness to painful and non-painful stimuli are dependent upon the stimulation method. Pain 53:255-264) or by radiant heat means using infra-red (see: Hardy J D, Wolff H G, Goodell H (1952), Pain Sensations and Reactions, Williams and Wilkins Co, Baltimore, 1952; and see: Lipman J J, Blumenkopf B and Parris W C V (1987) Chronic pain assessment using heatbeam dolorimetry. Pain 30:59-67) or laser irradiation (Svensson et al., (1991) xe2x80x9cComparison of four laser types for experimental pain stimulation on oral mucosa and hairy skin,xe2x80x9d Lasers in Surgery and Medicine 11:313-324). Radiant heal methods of generating the stimulus to be used in pain threshold measurement may themselves be of either contact or non-contact application. Thus, one skin-contacting method proposed as suitable for forearm testing uses a horizontal glass plate on which the user rests their arm and through which a radiant beam of heat is directed (see Hargreaves et al., U.S. Pat. No. 5,025,796, Apparatus and Methods for determining in vivo response to thermal stimulation in an unrestrained subject). Likewise, a non-contact method (Hardy et al, ibid) has been used in pain threshold measurement at various body sites.
For measurement of the thresholds of cutaneous sensory pain-evoking modalities, of pressure, of mechanoceptive tactile sensibility, of heat pain and of electrical pain, the skin-contacting types of devices (here called xe2x80x9ccontact devicesxe2x80x9d) are both convenient to use and adequate in interpretation. In measurement of pain tolerance limits, however, devices which stimulate more than one modality (touch and heat, for instance) interfere with the sensory perception of each discrete sensory mode. Thus, pain tolerance to a heat (thermal) stimulus is altered by mechanoceptor (touch) stimulation. In measuring thermal pain tolerance, a skin-contacting method of heat delivery cannot be used, therefore and a pure unimodal non-contact stimulus is absolutely necessary. Prior inventions have addressed the problem of pressure (touch stimulation) interference on thermal pain sensibility by attempting to control and standardize the degree of pressure applied by the heat-delivering element (see Guillemin, U.S. Pat. No. 2,728,337) but the ideal solution to the problem of sensory interference is to be found in completely obviating the confounding non-thermal stimulus entirely.
The HBD device and method was developed to take advantage of this non-contact sensory requirement of pain tolerance measurementxe2x80x94the device stimulating the subject""s skin by means of radiant heat and light without interfering mechanoceptor (touch sensation) stimulation. An earlier version has been described in which a radiant beam of heat and light, carefully calibrated and of constant power output and hence stimulus energy characteristics, employs two focused visible lasers to position the device at the correct distance from the skin, yet which may be carefully hand-held, and which employs a remote-sensing thermocouple to measure skin temperature during stimulus application (Lipman, U.S. Pat. No. 5,941,833 Heatbeam Dolorimeter for Pain and Sensory Evaluation). This Basic HBD device is mounted on a spring-loaded articulated support arm and is manually positioned by the operator at the appropriate distance from the various test sites around the body of the subject.
There remains a need however, fulfilled by the present invention, for an improved hand-held form of the above-described xe2x80x9cbasic Heatbeam Dolorimeterxe2x80x9d device that can be conveniently employed in situations where examination room space is limited and an articulated positioning arm inconvenient. The ideal improvement would render the HBD capable of automatically maintaining the proper skin-heating stimulus characteristics even under conditions where the operator""s hand may tremble or move or may spatially drift toward or away from the skin during the application of the stimulus. Because of the inverse square law, which applies to radiant EMR including that which generates heat, such inadvertent movement of a constant-power heat radiator would greatly increase skin heating rate as the device moved toward the skin and greatly decrease such rate as the device moved away. Movement in either direction would invalidate the measurement of pain tolerance limit.
The present invention overcomes these deficiencies in the prior art. The invention capitalizes on the constant and reliable relationship of distance and intensity that characterizes EMR propagation over distance and the speed and accuracy of distance measurement using sonar at short ranges. Therefore, the present invention provides a device and method which delivers EMR, such as heat, in an automatically controlled feedback manner, based on distance measurements of a sonar sensor. Additionally, the present invention fulfils a need for an improved hand-held form of the device, which is convenient to maintain at an appropriate and constant distance without the assistance of an articulated arm.
Lipman, U.S. Pat. No. 5,941,833 entitled: xe2x80x9cHeatbeam Dolorimeter for Pain and Sensory Evaluationxe2x80x9d describes a heat beam dolorimeter for measuring pain tolerance. The dolorimeter is mounted on a spring-loaded articulated support arm and is manually positioned by the operator at the appropriate distance from the various test sites around the body.
Hargreaves et al, U.S. Pat. No. 5,025,796 entitled xe2x80x9cApparatus and Methods for determining in vivo response to thermal stimulation in an unrestrained subjectxe2x80x9d describes a radiant heat pain stimulator that for adjustment of emitter-target distance relies on contact with the skin of the target site either by a wire cage or by a glass sheet on which the test animal or person rests.
Guillemin, U.S. Pat. No. 2,782,337 entitled xe2x80x9cDiagnostic Apparatusxe2x80x9d describes a contact-type heat stimulator which attempts to control the interfering effect of variation in pressure by regulating the degree of pressure applied.
Belanger, et al. U.S. Pat. No. 4,817,301 entitled xe2x80x9cApparatus for drying vehiclesxe2x80x9d describes a sonar-directed control means for positioning an air dryer nozzle in relation to a vehicle being dried.
Wentworth, U.S. Pat. No. 5,722,104 entitled xe2x80x9cPosition control system for counterweighted vehicle laundry top brushxe2x80x9d describes the use of a sonar method to control the position of a brush used to wash vehicles.
Springer, U.S. Pat. No. 5,765,995 entitled xe2x80x9cAutomated engine-powered pump control systemxe2x80x9d describes the application of a sonar sensing system in detecting water level drained by a pump.
Massa, U.S. Pat. No. 4,103,309 entitled xe2x80x98Automatic camera focusing meansxe2x80x99 describes a method of automatically controlling a movie camera focusing device by a sonar device measuring distance to the object photographed.
The present invention provides a device and method which delivers EMR, such as heat, in an automatically controlled feedback manner, based on distance measurements of a distance sensor. In a preferred embodiment, the device is a sonar-regulated Heat Beam Dolorimeter (HBD), a human cutaneous sensory testing device, capable of hand-held operation in a non-contact manner in the elicitation and measurement of the pain tolerance limit.
A first general embodiment of the invention provides a non-contact apparatus for regulating the delivery of electro-magnetic radiation to a target site, said apparatus comprising:
a non-contact emitter;
a distance sensor; and
an emitter control device, wherein said delivery of electromagnetic radiation is automatically regulated as a function of target-site distance through interaction of the distance sensor and the emitter control device.
In a preferred embodiment of the first general embodiment of the invention, the distance sensor is a sonar ranging sensor. In another preferred embodiment, the automatic regulation of the projection of electro-magnetic radiation provides a controlled effect at the target site when target-site distance changes within an effective control range. In another preferred embodiment, the electro-magnetic radiation comprises infrared radiation and the distance sensor is a non-infrared laser.
In another preferred embodiment of the first general embodiment the non-contact emitter is a radiant heat source, the distance sensor is a sonar-ranging sensor, and the emitter control device is a radiant heat source control device. In this embodiment, preferably said apparatus provides an automatically controlled heating rate at the target site when the target-site distance changes but remains within an effective distance range. In this embodiment, preferably the target site is a site on a subject""s skin and the apparatus is a dolorimeter for determining pain tolerance, said apparatus further comprising a non-contact temperature-measuring device, wherein said apparatus is capable of being employed for determining pain tolerance without tactile stimulation of the site on the subject""s skin by said apparatus or by any other means. Preferably, the apparatus further comprises a hand-held fixture, wherein the dolorimeter is capable of being held by a dolorimeter operator.
In a second general embodiment, the invention is a method for regulating the delivery of heat to a target site comprising the steps of:
(a) delivering electro-magnetic radiation;
(b) determining a target-site distance during the step of delivering electro-magnetic radiation; and
(c) automatically regulating the delivery of electromagnetic radiation as a function of the target-site distance.
In this method, preferably the step of determining the target-site distance utilizes sonar and the step of automatically regulating the projection of heat provides a controlled effect at the target site when the target-site distance changes but remains within an effective distance range. In another preferred embodiment the step of delivering electro-magnetic radiation comprises delivering infrared radiation and the step of determining the target-site distance utilizes a non-infrared laser beam.
In another preferred embodiment the step of delivering electro-magnetic radiation comprises delivering radiant heat and the step of determining the target-site distance utilizes sonar. Preferably, said step of automatically regulating provides a controlled effect at the target site when the target-site distance changes within an effective control range. In a further preferred embodiment the target site is a site on a subject""s skin, said method further comprising determining temperature of the target site without contacting the target site, wherein said method is capable of determining pain tolerance without tactile stimulation of the site on the subject""s skin. In a further preferred embodiment, the method further comprises providing an apparatus for carrying out the steps of delivering radiant heat, determining the target-site distance, automatically regulating the projection of heat, and determining the temperature of the target site. Preferably the apparatus allows the method to be carried out while the dolorimeter is held by a dolorimeter operator.
In another preferred embodiment of the first general embodiment the non-contact emitter is a light source, the distance sensor is a sonar ranging sensor, and the emitter control device is a light source control device. Where the non-contact emitter is a light source, preferably the apparatus provides a controlled amount of energy at the target site when the distance of the light source to the target site changes but remains within an effective distance range.